Homemade bomb explodes on packed London subway

British police arrested a second man over the bombing of a London commuter train on Friday that injured 30 people and the security services lowered the threat level for an attack from its highest setting.

The 21-year-old man was detained under Britain’s terrorism laws in the west London suburb of Hounslow just before midnight on Saturday, London police said in a statement.

Police earlier arrested an 18-year-old man in the departure lounge of Dover port in what they called a “significant” step and then raided a property in Sunbury-on-Thames, a town near London and about four miles (six km) from Hounslow.

The home-made bomb shot flames through a packed carriage at west London’s Parsons Green Tube station during the Friday morning rush hour but apparently failed to detonate fully.

Islamic State claimed responsibility, as it has for other attacks in Britain this year, including two in London and one at a concert by American singer Ariana Grande in Manchester in May. (Reuters)

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Homemade bomb explodes on packed London subway

Police officers on the scene during a search on an address in Stanwell on Sept. 17, 2017 in London, England. A second man has today been arrested in connection with the Parsons Green attack which left 30 injured. (Photo: Jack Taylor/Getty Images)

Homemade bomb explodes on packed London subway

Police and forensic officers work at a property in Sunbury-on-Thames, southwest London, as part of the investigation into Friday’s Parsons Green bombing, Saturday Sept, 16, 2017. British police made what they called a “significant” arrest Saturday in southern England following the partially exploded bomb attack on the London subway. (Photo: Victoria Jones/PA via AP)

Homemade bomb explodes on packed London subway

Police officers work near a property in Sunbury-on-Thames, southwest London, as part of the investigation into Friday’s Parsons Green bombing, Saturday Sept, 16, 2017. (Photo: Victoria Jones/PA via AP)

Homemade bomb explodes on packed London subway

A passenger walks onto the platform at Parsons Green subway station after it was reopened following a terrorist attack on a train at the station yesterday in London, Saturday, Sept. 16, 2017. (Photo: Tim Ireland/AP)

Homemade bomb explodes on packed London subway

Police forensics officers works alongside an underground tube train at a platform at Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. (Photo: Adrian Dennis/AFP/Getty Images)

Homemade bomb explodes on packed London subway

People react near Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Hannah McKay/Reuters)

Homemade bomb explodes on packed London subway

Emergency services attend to the scene near Parsons Green Underground Station on Sept. 15, 2017 in London, England. (Photo: Jack Taylor/Getty Images)

Homemade bomb explodes on packed London subway

Personal belonglongs and a bucket with an item on fire inside it, are seen on the floor of an underground train carriage at Parsons Green station in West London, Britain, Sept. 15, 2017, in this image taken from social media. (Photo: Sylvain Pennec via Reuters)

Homemade bomb explodes on packed London subway

Members of the emergency services work near Parsons Green underground tube station in west London on Sept. 15, 2017, following an incident on an underground tube carriage at the station. (Photo: Daniel Leal-Olivas/AFP/Getty Images)

Homemade bomb explodes on packed London subway

An injured woman is led away after an incident at Parsons Green underground station in London, Britain, Sept. 15, 2017. (Photo: Luke MacGregor/Reuters)

Homemade bomb explodes on packed London subway

Armed police officers walk through a carriage of a London underground tube train at Parsons Green station in London, Britain, Sept. 15, 2017. (Photo: Hannah McKay/Reuters)

Homemade bomb explodes on packed London subway

A woman reacts outside Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Kevin Coombs/Reuters)

Homemade bomb explodes on packed London subway

In this aerial image made from video, police officers work at the Parsons Green Underground Station after an explosion in London Friday, Sept. 15, 2017. (Photo: Pool via AP)

Homemade bomb explodes on packed London subway

Police with dogs keep watch over FC Koln fans during the Europa League match against Arsenal at the Emirates Stadium, London, Thursday Sept. 14, 2017. (Photo: Nick Potts/PA via AP)

Homemade bomb explodes on packed London subway

In this image made from video, a woman with blankets wrapped around her is being escorted by emergency services near the scene of an explosion in London Friday, Sept. 15, 2017. (Photo: Sky via AP)

Homemade bomb explodes on packed London subway

Police and an ambulance stand near Parsons Green subway station in London, Friday, Sept. 15, 2017. (Photo: Frank Augstein/AP)

Homemade bomb explodes on packed London subway

A police officer holds cordon tape near Parsons Green subway station in London, Friday, Sept. 15, 2017. (Photo: Frank Augstein/AP)

Homemade bomb explodes on packed London subway

A woman walks with her child past police cordon near Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Hannah McKay/Reuters)

Homemade bomb explodes on packed London subway

Police officers escort members of the public out of their inner cordon as they work near Parsons Green underground tube station in west London on Sept.15, 2017, following an incident on an underground tube carriage at the station. (Photo: Daniel Leal-Olivas/AFP/Getty Images)

Homemade bomb explodes on packed London subway

A forensics officer on the platform at Parsons Green station in west London after Scotland Yard declared a terrorist incident following a blast which sent a “fireball” and a “wall of flame” through a packed London Underground train. Friday, Sept. 15, 2017. (Photo: Dominic Lipinski/PA via AP)

Homemade bomb explodes on packed London subway

A police officer escorts an injured woman from the scene at Parsons Green Underground Station on September 15, 2017 in London, England. (Photo: Chris J Ratcliffe/Getty Images)

Homemade bomb explodes on packed London subway

In this aerial image made from video, emergency workers help people to disembark a train near the Parsons Green Underground Station after an explosion in London Friday, Sept. 15, 2017. (Photo: Pool via AP)

Homemade bomb explodes on packed London subway

Members of the emergency services work near Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. (Photo: Daniel Leal-Olivas/AFP/Getty Images)

Homemade bomb explodes on packed London subway

Forensic officers are seen at Parsons Green Underground Station on Sept.15, 2017 in London, England. (Photo: Jack Taylor/Getty Images)

Homemade bomb explodes on packed London subway

A woman walks with her child past police cordon near Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Hannah McKay/Reuters)

Homemade bomb explodes on packed London subway

Police officers walk on the road near Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Kevin Coombs/Reuters)

Homemade bomb explodes on packed London subway

An injured woman reacts outside Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Kevin Coombs/Reuters)

Homemade bomb explodes on packed London subway

Police, fire and ambulance crew attend to an incident at Parsons Green underground station in London, Britain, Sept. 15, 2017. (Photo: Luke MacGregor/Reuters)

Homemade bomb explodes on packed London subway

Police, fire and ambulance crew attend to an incident at Parsons Green underground station in London, Britain, Sept. 15, 2017. (Photo: Luke MacGregor/Reuters)

Homemade bomb explodes on packed London subway

Armed policemen stand by cordon near Parsons Green tube station in London, Britain, Sept. 15, 2017. (Photo: Hannah McKay/Reuters)

Homemade bomb explodes on packed London subway

Deputy Chief Constable Adrian Hanstock of the British Transport Police makes a statement to the media after an incident at Parsons Green underground station in London, Britain, Sept. 15, 2017. (Photo: Luke MacGregor/Reuters)

Homemade bomb explodes on packed London subway

A police forensic officer stands beside the train, at left, where an incident happened, that police say they are investigating as a terrorist attack, at Parsons Green subway station in London, Friday, Sept. 15, 2017. (Photo: Frank Augstein/AP)